1. Field of the Invention
This invention relates to a rotary and reciprocating device and more particularly to a rotary and reciprocating drive device used in, such as, for example, wiper devices for vehicle windshields.
2. Statement of Prior Art
As an example of a conventional rotary and reciprocating drive device, a windshield wiper device is shown in FIGS. 7 and 8, wherein, wiper blade 2 is rotatable in a predetermined or wiped area on a windshield 1 and also is in contact therewith with a certain pressure. The blade 2 is supported on a wiper arm 3 which is rotatably mounted on a drive arm 5 through a pin 6. The drive arm 5 is secured to a top end of a rotatable shaft 4 as is clearly shown in FIG. 7. A bell crank 7 is rotatably mounted on the drive arm 5 through pin 7a. A spring 8 is disposed between one end of the wiper arm 3 and end of the bell crank 7.
The rotatable shaft 4 is rotatably supported on a bracket 9 through bearings. The bracket 9 is secured to a vehicle fixed part. The lower end of the shaft 4 is connected to a link 10 for unitary rotation when the link 10 is rotated. This movement is then transmitted to the drive arm 5 to rotate the same and further to the wiper blade 2 via the wiper arm 3 thereby to wipe the outer surface of the windshield 1 with a rubber blade on the wiper blade 2.
A central bore is provided in the rotatable shaft 4 and a rod 11 is inserted into the bore and extending to be in contact with the other end of the bell crank 7 at one end. A rack 12 is provided at the other end of the rod 11 to be in engagement with a pinion 13 which is secured on the bracket 9.
When the contact pressure between the windshield 1 and the wiper blade 2 has to be changed for adjustment, the pinion 13 is rotated to move the rod 11 in axial direction to rotate the bell crank 7 around the pin 7a thereby to change the biasing force of spring 8. In order to change the contact pressure between the windshield 1 and the wiper blade 2, it is necessary to move rod 11 in axial direction to rotate the bell crank 7. The thrust force P needed to rotate the pinion 13 should be sufficient for overcoming the moment Ps X1 (see FIG. 8 in which the bell crank 7 is being rotated to the position illustrated with the imaginary line).